ABSTRACT:

Recently it was proposed how we can learn about the stress tensor inside hadrons through the interpretation of one of the form factors of the energy-momentum tensor, D(t), which is related to the "D-term." This promises interesting insights on the internal forces inside hadronic bound states and allows us to formulate questions like: what is the "pressure" inside the proton?

Or what is the "mechanical radius" of the proton? The physical meaning of the D-term form factor D(t) will be discussed.

The recent progress in theory, the latest experimental results, and their applications will be reviewed.